EP0403467A2 - Anti-aliasing optisches System - Google Patents

Anti-aliasing optisches System Download PDF

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Publication number
EP0403467A2
EP0403467A2 EP90890178A EP90890178A EP0403467A2 EP 0403467 A2 EP0403467 A2 EP 0403467A2 EP 90890178 A EP90890178 A EP 90890178A EP 90890178 A EP90890178 A EP 90890178A EP 0403467 A2 EP0403467 A2 EP 0403467A2
Authority
EP
European Patent Office
Prior art keywords
optical
low
aliasing
pass filter
pyramidal structure
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90890178A
Other languages
English (en)
French (fr)
Other versions
EP0403467A3 (de
Inventor
William T. Plummer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Polaroid Corp
Original Assignee
Polaroid Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Polaroid Corp filed Critical Polaroid Corp
Publication of EP0403467A2 publication Critical patent/EP0403467A2/de
Publication of EP0403467A3 publication Critical patent/EP0403467A3/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
    • G02B27/46—Systems using spatial filters

Definitions

  • the present invention pertains to an optical, low-pass filter, anti-aliasing apparatus and, in particular, to an optical, low-pass filter, anti-aliasing apparatus for use with a focal plane array such as an image sensing device, for example, a solid-state image sensing device using a CCD (charge-coupled device) or the like, which produces a predetermined image pickup output by carrying out spatial sampling.
  • a focal plane array such as an image sensing device, for example, a solid-state image sensing device using a CCD (charge-coupled device) or the like, which produces a predetermined image pickup output by carrying out spatial sampling.
  • a color video camera typically produces a color signal output corresponding to the viewed object scene by color coding an image of the object scene with a color filter which is disposed at the front of the video camera and by spatially sampling each color using an array of photosensitive elements such as, for example, a CCD, as a solid-state image sensing device.
  • a CCD photosensitive elements
  • an imaging system it is well known that components in the object scene which contain frequencies too large to be analyzed with the sampling interval used contribute to the amplitudes of lower frequency components and produce, thereby, image errors which are referred to in the art as aliasing distortion or undersampling artifacts.
  • an optical system for the array can eliminate aliasing if it has a frequency response which cuts out the higher frequency content of the object scene.
  • an optical apparatus such as, for example, a birefringent blur filter has become a common component in consumer color video cameras.
  • Such apparatus are typically placed between a lens and the photosensor array to provide a low-pass filter function which reduces the spatial frequency content of the object scene at frequencies above the Nyquist frequency of the photosensor array to make the imaging system less susceptible to aliasing distortion.
  • an achromatic low-pass filter or "blur" is effective in minimizing aliasing distortion.
  • optical low-pass filter for a Single-Vidicon Color Television Camera
  • M. Mino and Y. Okano in Journal of the SMPTE , Vol. 81, April, 1972, pp. 282-285 describes several desirable conditions which an optical low-pass filter used to remove aliasing distortion should satisfy.
  • one condition is that the optical low-pass filter should preferably be a phase filter which does not diminish the light level in the transmitted light.
  • Another condition for the optical low-pass filter is that its effect should be independent of the aperture of the optical imaging system. In addition to these conditions, one may add the condition that the optical low-pass filter be easily manufactured at a relatively low cost.
  • an aliasing suppression phase filter which is commonly used in commercially available video cameras is a birefringent blur filter.
  • a birefringent blur filter is typically made of crystalline quartz wherein the crystal axis of the filter plates are oriented at about a 45° angle with respect to the surface. In this orientation, the birefringent quartz exhibits the double-refraction effect, and an unpolarized input ray passing into the filter emerges as two polarized output rays.
  • This type of filter suffers from the drawback that it is rather expensive, and it is also rather complicated to manufacture.
  • optical noise phase filter which is comprised of statistically distributed phase elements.
  • the optical noise filter suffers from a drawback in that it becomes difficult for the phase elements to be distributed statistically as the aperture stop of the objective lens of the imaging system is reduced.
  • phase diffraction grating can be used as a frequency selective filter.
  • a grating is frequency selective, and the size of the grating is restricted by the objective aperture stop.
  • gratings are rather expensive and are also rather complicated to manufacture.
  • Embodiments of the present invention satisfy the above-described need by providing a wavelength independent, optical, low-pass phase filter which is effective at substantially all aperture stops of an optical imaging system and which is relatively simple and inexpensive to manufacture.
  • an embodiment of the inventive optical apparatus comprises a substantially transparent, convex, pyramidal structure comprised of four shallow, wedge-like protrusions or a substantially transparent, concave, pyramidal structure comprised of four shallow, wedge-like depressions.
  • the wedge-like protrusions of the pyramidal structure are formed from barium fluoride (BaF2) which has been coated with magnesium fluoride (MgF2) to prevent absorption of H2O.
  • BaF2 barium fluoride
  • MgF2 magnesium fluoride
  • the pyramidal structure may be formed on a glass plate, a plastic plate or even on the surface of a lens.
  • the pyramidal structure may be fabricated by pressing a softened material as, for example, a plastic material against a harder surface coating of a structure having a form which will provide either the desired convex or concave pyramidal structure in the softened material.
  • the inventive apparatus is preferably used by placing it in the aperture stop plane or its image where the iris would also be conveniently located for an optical imaging system. This placement ensures that the iris of the aperture stop can be opened or closed while the inventive apparatus provides substantially the same amount of low-pass filtering action.
  • the wedge angle of a particular wedge portion of the inventive pyramidal structure determines the amount by which the light passing therethrough is shifted in direction.
  • wedges disposed on opposite sides of the inventive pyramidal structure will shift the light passing therethrough in opposite directions.
  • the wedge angles of the pyramidal structure are made large enough to shift the light passing through the structure so that on average it impinges simultaneously on several pixels or sensors in the photosensor array. This causes a blurring effect which provides a spatial low-pass filter.
  • apparatus 100 comprises wedges or tetrahedra 101-104 which are disposed on glass plate 110.
  • Wedges 101- 104 are comprised of barium fluoride (BaF2) which has been coated with a layer of magnesium flouride (MgF2) to prevent the absorption of H2O.
  • BaF2 barium fluoride
  • MgF2 magnesium flouride
  • Pyramidal apparatus 100 is fabricated in accordance with methods well known to those of ordinary skill in the art. Specifically, in one embodiment, pyramidal apparatus 100 is formed by vacuum depositing BaF2 upon glass plate 110 through a square mask. The aperture provided by the square mask is gradually diminished so that the area of glass plate 110 which is exposed to vacuum deposition of the BaF2 is also gradually diminished. Then, in accordance with methods well known to those of ordinary skill in the art, an MgF2 coating is applied to the BaF2 pyramid structure by vacuum deposition. As one can readily appreciate, this method of fabrication provides a optical apparatus which is substantially wavelength independent and which is substantially transparent to light passing therethrough.
  • FIG. 2 shows optical apparatus 100 disposed in aperture stop plane 150, substantially at the iris, of an optical system 200.
  • Optical system 200 is used to image an object scene onto photosensor array 250 which is comprised of spaced apart photosensor elements, also referred to as pixels.
  • apparatus 100 is placed at the opening of adjustable iris in the form of two counter-reciprocating shutter blades 190 located substantially at or near the aperture stop plane 150 between senses 170 and 180 of optical system 200. Diverging lens 180 spreads the light passing between lens 160 and 170 a sufficient amount so that substantially one-quarter of the incident light which passes through optical system 200 passes through each of wedges 101-104 of apparatus 100.
  • adjustable iris 190 at aperture stop plane 150 of optical system 200 can be opened or closed while apparatus 100 provides substantially the same amount of low-pass filtering action.
  • each wedge 101-104 of inventive apparatus 100 Approximately one-quarter of the incident light passes through each wedge 101-104 of inventive apparatus 100, and the wedge angle of each wedge determines the amount by which the light passing therethrough is shifted in direction.
  • wedges disposed on opposite sides of apparatus 100 for example, wedges 101 and 103 and wedges 102 and 104, shift the light passing therethrough in opposite directions.
  • the light which passes through apparatus 100 is shifted so that it impinges, on the average, simultaneously upon several elements or pixels in photosensor array 250.
  • This causes a blurring effect which provides a spatial low-pass filter. That is, light from an object scene which passes through each of the wedges is angled slightly away from light which passes through the other wedges.
  • the thickness of wedges 101-104 at the center and, hence, the wedge angles is made to be sufficiently large so that the desired blur of light which passes therethrough is obtained at photosensor array 250.
  • an embodiment of the present invention which comprises a substantially transparent, convex, pyramidal structure comprised of four shallow, wedge-like protrusions
  • the present invention is not limited to such embodiments.
  • further embodiments of the present invention comprise a substantially transparent, concave, pyramidal structure comprised of four shallow, wedge-like depressions.
  • embodiments of the convex or concave inventive pyramidal structure may be fabricated by pressing a softened material such as, for example, a plastic material, against a harder surface coating of a structure having a form which will provide either the desired convex or concave pyramidal structure in the softened material.
  • a softened material such as, for example, a plastic material
  • embodiments of the present invention are not limited to the formation of a pyramidal structure upon or in a plate and, in fact, further embodiments of the present invention comprise the formation of the pyramidal structure directly on a lens.
  • wedges may each be fabricated separately and glued together to provide a convex, pyramidal structure. In such a case, it is advantageous to polish the outer surface of the completed apparatus after the pieces have been joined.
  • the pyramid For use with very small apertures, such that the diffraction blur of the aperture itself can accomplish the anti-aliasing function, the pyramid would be flattened at the very center, forming a frustrum.
EP19900890178 1989-06-12 1990-06-07 Anti-aliasing optisches System Withdrawn EP0403467A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US364658 1989-06-12
US07/364,658 US4989959A (en) 1989-06-12 1989-06-12 Anti-aliasing optical system with pyramidal transparent structure

Publications (2)

Publication Number Publication Date
EP0403467A2 true EP0403467A2 (de) 1990-12-19
EP0403467A3 EP0403467A3 (de) 1991-03-06

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19900890178 Withdrawn EP0403467A3 (de) 1989-06-12 1990-06-07 Anti-aliasing optisches System

Country Status (7)

Country Link
US (1) US4989959A (de)
EP (1) EP0403467A3 (de)
JP (1) JPH0355981A (de)
CA (1) CA2016058A1 (de)
DE (1) DE403467T1 (de)
ES (1) ES2020796A4 (de)
GR (1) GR910300012T1 (de)

Cited By (3)

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WO2003079093A2 (en) * 2002-03-14 2003-09-25 Science & Engineering Associates, Inc. Multiple imaging system and method for designing same
WO2007137293A2 (en) * 2006-05-23 2007-11-29 Omnivision Cdm Optics, Inc. Saturation optics
KR101475529B1 (ko) 2006-04-17 2014-12-23 옴니비젼 씨디엠 옵틱스 인코퍼레이티드 배열 이미징 시스템 및 관련 방법

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JP3506144B2 (ja) * 1992-10-19 2004-03-15 ソニー株式会社 画像表示装置及び表示デバイス用光学フィルタ
US5438366A (en) * 1993-03-31 1995-08-01 Eastman Kodak Company Aspherical blur filter for reducing artifacts in imaging apparatus
US5322998A (en) * 1993-03-31 1994-06-21 Eastman Kodak Company Conical blur filter for reducing artifacts in imaging apparatus
US5299275A (en) * 1993-03-31 1994-03-29 Eastman Kodak Company Optical fiber filter for reducing artifacts in imaging apparatus
US5541653A (en) * 1993-07-27 1996-07-30 Sri International Method and appartus for increasing resolution of digital color images using correlated decoding
US5353728A (en) * 1993-12-17 1994-10-11 Marine Safety Systems Inc. Centrally-located-ballast-tank vessel
US6025873A (en) * 1994-04-07 2000-02-15 Olympus Optical Co., Ltd. Endoscope system provided with low-pass filter for moire removal
JPH0821991A (ja) 1994-07-08 1996-01-23 Sony Corp 画像表示装置
US20020118457A1 (en) * 2000-12-22 2002-08-29 Dowski Edward Raymond Wavefront coded imaging systems
US6911638B2 (en) 1995-02-03 2005-06-28 The Regents Of The University Of Colorado, A Body Corporate Wavefront coding zoom lens imaging systems
US7218448B1 (en) * 1997-03-17 2007-05-15 The Regents Of The University Of Colorado Extended depth of field optical systems
US20020195548A1 (en) * 2001-06-06 2002-12-26 Dowski Edward Raymond Wavefront coding interference contrast imaging systems
US5682266A (en) * 1995-04-05 1997-10-28 Eastman Kodak Company Blur filter for eliminating aliasing in electrically sampled images
US5684293A (en) * 1995-11-29 1997-11-04 Eastman Kodak Company Anti-aliasing low-pass blur filter for reducing artifacts in imaging apparatus
US5696371A (en) * 1996-05-23 1997-12-09 Eastman Kodak Company Diffractive/refractive lenslet array
US5751492A (en) * 1996-06-14 1998-05-12 Eastman Kodak Company Diffractive/Refractive lenslet array incorporating a second aspheric surface
US6937283B1 (en) 1996-12-03 2005-08-30 Eastman Kodak Company Anti-aliasing low-pass blur filter for reducing artifacts in imaging apparatus
US6040857A (en) * 1997-05-27 2000-03-21 Eastman Kodak Company Phase-noise type broad spectral bandwidth optical low-pass anti-aliasing filter
US6326998B1 (en) * 1997-10-08 2001-12-04 Eastman Kodak Company Optical blur filter having a four-feature pattern
US6021005A (en) * 1998-01-09 2000-02-01 University Technology Corporation Anti-aliasing apparatus and methods for optical imaging
JP2000089114A (ja) * 1998-09-08 2000-03-31 Olympus Optical Co Ltd ズームレンズ
US6536898B1 (en) * 2000-09-15 2003-03-25 The Regents Of The University Of Colorado Extended depth of field optics for human vision
US6873733B2 (en) 2001-01-19 2005-03-29 The Regents Of The University Of Colorado Combined wavefront coding and amplitude contrast imaging systems
US6842297B2 (en) 2001-08-31 2005-01-11 Cdm Optics, Inc. Wavefront coding optics
US7164807B2 (en) * 2003-04-24 2007-01-16 Eastman Kodak Company Method and system for automatically reducing aliasing artifacts
US7171055B2 (en) * 2003-04-24 2007-01-30 Eastman Kodak Company Parametric means for reducing aliasing artifacts
US7321112B2 (en) * 2003-08-18 2008-01-22 Gentex Corporation Optical elements, related manufacturing methods and assemblies incorporating optical elements
US20090096915A1 (en) * 2007-10-16 2009-04-16 Kelly Sean C Anti-aliasing spatial filter system
WO2009066770A1 (ja) * 2007-11-22 2009-05-28 Nikon Corporation デジタルカメラおよびデジタルカメラシステム

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WO2003079093A3 (en) * 2002-03-14 2004-04-15 Science & Engineering Associat Multiple imaging system and method for designing same
US7177085B2 (en) 2002-03-14 2007-02-13 Science & Engineering Associates, Inc. Multiple imaging system and method for designing same
KR101475529B1 (ko) 2006-04-17 2014-12-23 옴니비젼 씨디엠 옵틱스 인코퍼레이티드 배열 이미징 시스템 및 관련 방법
WO2007137293A2 (en) * 2006-05-23 2007-11-29 Omnivision Cdm Optics, Inc. Saturation optics
WO2007137293A3 (en) * 2006-05-23 2008-03-27 Cdm Optics Inc Saturation optics
EP2256538A1 (de) * 2006-05-23 2010-12-01 OmniVision CDM Optics, Inc. Optisches System mit segmentierter Pupillenfunktion
US8164040B2 (en) 2006-05-23 2012-04-24 Omnivision Technologies, Inc. Saturation optics
CN101449195B (zh) * 2006-05-23 2013-04-10 全视技术有限公司 饱和光学器件
KR101305868B1 (ko) * 2006-05-23 2013-09-09 옴니비젼 씨디엠 옵틱스 인코퍼레이티드 포화 광학계
TWI447502B (zh) * 2006-05-23 2014-08-01 Omnivision Tech Inc 成像電磁能之成像系統、相位修改光學及設計瞳孔函數之方法

Also Published As

Publication number Publication date
DE403467T1 (de) 1991-04-11
GR910300012T1 (en) 1991-11-15
JPH0355981A (ja) 1991-03-11
ES2020796A4 (es) 1991-10-01
US4989959A (en) 1991-02-05
EP0403467A3 (de) 1991-03-06
CA2016058A1 (en) 1990-12-12

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